Specific Secretion of Citric Acid Induced by Al Stress in Cassia tora L.
Open Access
- 1 January 1997
- journal article
- research article
- Published by Oxford University Press (OUP) in Plant and Cell Physiology
- Vol. 38 (9) , 1019-1025
- https://doi.org/10.1093/oxfordjournals.pcp.a029266
Abstract
A rapid and sensitive assay method for Al-chelating activity was established to screen Al-chelating substances secreted from roots of Al-resistant species in response to Al stress. From one Al-resistant species, Cassia tora L., an Al-chelating substance was detected in the root exudates when they were exposed to SO μM Al in 0.5 mM CaCl2 solution at pH 4.5; the dominant component was identified as citric acid. The secretion of citric acid was very low during the first 4 h after initiation of Al treatment, but increased markedly thereafter. A 3-h pulse with 50 μM Al also induced significant secretion of citric acid after 6 h. The lag between Al addition and secretion of citric acid suggests that inducible processes are involved. A dose-response experiment showed that the amount of secreted citric acid increased with increasing external concentrations of Al. Eight-d treatment of P deficiency did not induce the secretion of citric acid. Exposure to 50μM of either lanthanum (La3+) or ytterbium (Yb3+) did not induce the secretion of citric acid either. These findings indicate that the secretion of citric acid is a response specific to Al stress in .C. toraand constitutes a mechanism of Al resistance.Keywords
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